1. Field of the Invention
The present invention relates to an exhaust gas treating tower that is provided in various kinds of plants, boilers or the like.
2. Description of the Prior Art
In order to remove sulfur oxides (SO2) contained in the exhaust gas of various kinds of plants, boilers or the like, an exhaust gas treating tower of gas-liquid contact type is often used.
In the exhaust gas treating tower of this type, what is called a liquid column type is known in which absorbing liquid of the sulfur oxides is upwardly spouted in a column shape, as is known by the Japanese laid-open utility model laid-open application 1984-53828 (FIG. 1), for example. As shown in FIGS. 31 and 32 here, in such an exhaust gas treating tower 1 of liquid column type, the exhaust gas is introduced from an inlet port 2 formed in a lower side portion of the exhaust gas treating tower 1. While this exhaust gas is flowing up toward an outlet port 3 formed in an upper portion of the tower, it makes contact with liquid columns C spouted in the column shape and thereby the sulfur oxides contained in the exhaust gas is removed.
In the exhaust gas treating tower of liquid column type so constructed, fine liquid drops (generally called a mist) are contained in the exhaust gas that has made contact with the liquid columns C to be discharged from the outlet port 3 and in order to recover the mist, there is provided an eliminator 5 (FIG. 31) or a mist eliminator 6 (FIG. 32) at the outlet port 3.
In the above-mentioned exhaust gas treating tower 1 of liquid column type, in order to enhance the exhaust gas treating efficiency (treating quantity per unit time), it is necessary to make a large size plant or to increase the exhaust gas flow velocity. However, needless to mention, to make a large size plant is usually not preferable. Thus, to make the exhaust gas flow velocity higher than the present situation is considered. But in the conventional exhaust gas treating tower 1, as shown in FIG. 9, if the gas flow velocity is increased beyond a certain level, while the sulfur oxides cannot be sufficiently removed by the liquid columns C, the exhaust gas passes through the tower to be blown off outside as it is. Thus, there is a problem that the exhaust gas treating efficiency is hardly enhanced.
Also, in the example shown in FIG. 32, there will be caused a problem that while the liquid drops in the exhaust gas cannot be sufficiently recovered by the mist eliminator 6, the liquid drops together with the exhaust gas pass through the mist eliminator 6 to be discharged outside.
Here, as the exhaust gas flowing upward from below makes gas-liquid contact with the liquid columns C, the liquid drops generated in the vicinity of the liquid columns C receive an upward resisting force by the exhaust gas flow. According to the balance between the gravity force corresponding to the weight (diameter) of the liquid drops and the resisting force of the upwardly flowing exhaust gas (air resisting force), the liquid drops having a weight (diameter) beyond a certain level are entrained with the exhaust gas flow to move up toward the mist eliminator 6 in the exhaust gas treating tower 1.
At this time, if the flow velocity of the exhaust gas becomes higher, the upper limit of the diameter of the liquid drops moving up in the exhaust gas treating tower 1 becomes correspondingly larger and the quantity of the upwardly moving liquid drops also increases as a whole. Thus, the quantity of the liquid drops that must be collected in the mist eliminator 6 increases and the quantity of the liquid sticking to surfaces of collecting plates 6a of the mist eliminator 6 also increases.
On the other hand, while the flow velocity of the exhaust gas is high, the liquid sticking to the surfaces of the collecting plates 6a is again scattered by the exhaust gas, resulting in that the liquid passes through the mist eliminator 6.
When the exhaust gas treating tower 1 is to be designed, a flow velocity of the exhaust gas at a steady operation time is set and, based on the so set exhaust gas flow velocity, the diameter of the liquid drops that move up in the exhaust gas treating tower 1 together with the exhaust gas is obtained and the mist eliminator 6 is designed so that the liquid drops of the so obtained diameter can be securely collected.
Nevertheless, in the exhaust gas treating tower 1, the exhaust gas flow is not always uniform but due to various causes, the flow often becomes unsteady and the flow velocity becomes also different according to the place. For this reason, actually, there often exists such an area where the exhaust gas flows at a velocity higher than the designed flow velocity of the steady operation time. In this area, the liquid drops of a diameter larger than a presumed diameter at the time of design move up toward the mist eliminator 6 together with the exhaust gas and this likewise results in that the liquid is not sufficiently collected by the mist eliminator 6 but passes therethough.